The present invention relates generally to a foil-fluid bearing, and in particular, to a foil-fluid bearing comprising compliant supports.
Foil-air bearings are advantageous as they operate efficiently over a large temperature range, have increasing load capacity as rotational speeds increase, can handle severe environmental conditions, and are more reliable than rolling element bearings because they require fewer parts to support the rotating assemblies and do not need lubrication. However, they also require inherently tight tolerance controls on the bearings themselves and their housings in order to maintain a very close alignment between each radial bearing in a rotor system in order to operate effectively. Bearing misalignment can be caused by excessive manufacturing tolerances, operational loads or thermal distortion of the bearing housing, and can result in shaft angular misalignment causing unacceptable whirl instability. Existing foil-air bearings also require a good control of both radial stiffness and damping characteristics of the inner foil support structure.
The use of hydrodynamic fluid journal bearings having compliant foils is known. The inner foils of the bearing are arranged such that the end sections of the foils themselves are more compliant than the central section of the foils, and can deflect independently in order to provide improved conformity to a misaligned rotor supported by the bearing. Strong misalignment forces can thereby be tolerated. U.S. Pat. No. 4,274,683 teaches such a compliant foil bearing. However, these hydrodynamic journal bearings require metallic corrugated foil assemblies that are comprised of several separate sections of foils, which must each be independently flexible and able to deflect different controlled amounts. Introducing independent flexibility to the metallic foils themselves considerably adds to the complexity, and consequently cost, of the bearing. Additionally, as each bearing requires several discrete metallic foil sections having different flexibility, the complexity and manufacturing costs are further increased.
There remains a need to provide a foil-fluid bearing capable of tolerating angular misalignment, without significantly adding complexity to the internal construction of the bearing, and consequently without significantly adding to material and manufacturing costs.
It is an object of the present invention to provide an improved foil-fluid bearing capable of increased angular misalignment tolerance.
It is an object of the present invention to provide a foil-fluid bearing having a simplified compliant support arrangement.
Therefore, in accordance with the present invention, there is provided a foil-fluid bearing assembly adapted for supporting a shaft within an outer bearing housing, the foil-fluid bearing assembly comprising: a bearing sleeve having an outer surface and an inner circumferential surface diametrically sized to receive the shaft therewithin such that an annular clearance gap is radially defined between an outer surface of the shaft and the inner circumferential surface, the annular clearance gap adapted for accommodating fluid therein and axially extending along a substantial portion of a length of the bearing sleeve; a foil element disposed within the annular clearance gap; a compliant bearing support contiguously disposed between the outer surface of the bearing sleeve and the outer bearing housing, and permitting elastic deflection of the compliant bearing support, independent of movement of the foil element; and the compliant bearing support comprising at least two independent compliant support elements respectively having a first and a second modulus of elasticity, wherein the first modulus of elasticity is less than the second modulus of elasticity; whereby angular misalignment capability for the foil-fluid bearing is provided by the compliant bearing support.
There is also provided, in accordance with the present invention, a foil-fluid bearing assembly adapted for rotatably supporting a shaft within a bearing housing, the foil-fluid bearing assembly comprising: a bearing sleeve having an outer surface and an inner surface defining an inner race, said inner race diametrically sized to receive a rotating shaft therewithin and maintain an annular clearance gap radially between said rotating shaft and said inner circumferential surface, the annular clearance gap axially extending along a substantial portion of a length of the bearing sleeve, the bearing sleeve adapted, in use, to supply a support fluid to substantially fill said annular clearance gap; a foil element circumferentially disposed between said inner race and said shaft; a compliant bearing support disposed between the outer surface of the bearing sleeve and the bearing housing; and the compliant bearing support having at least two independent compliant support elements, said at least two independent compliant support elements respectively having a first and a second modulus of elasticity, wherein the first modulus of elasticity is less than the second modulus of elasticity.
There is additionally provided, in accordance with the present invention, a foil-fluid bearing assembly comprising: a compliantly supported bearing sleeve, radially disposed between a rotating shaft and an outer housing, such that an annular clearance gap, adapted for receiving a support fluid therein, is provided between the rotating shaft and the bearing sleeve; a foil element being radially disposed within the annular clearance gap; the bearing sleeve being compliantly supported within the outer housing by at least two independent compliant supports, radially disposed between the bearing sleeve and the outer housing; and the two independent compliant supports respectively having a first and second modulus of elasticity, the first modulus of elasticity being less than the second modulus of elasticity.